The present invention relates to an optical component which is used for compensating the temperature dependent gain characteristic (a temperature dependency of gain) of an optical amplifier such as an EDFA (optical amplifier of the erbium-doped optical fiber type).
The evolution of the information-oriented society has set a tendency for the volume of telecommunications information to dramatically increase, therefore, progress toward a larger capacity and a faster speed in telecommunications using optical fibers is necessary and critical. An advantageous approach for a faster speed and a larger capacity is to use optical fibers doped with rare earths, such as erbium-doped optical fibers. Use of an erbium-doped optical fiber has led to development of an optical amplifier of the optical fiber amplifier type which can amplify a light signal as which remains as light, and the development of an optical amplifier of the optical fiber amplifier type has led to increasingly rapid ongoing development of large-capacity communications and long distance transmissions.
Another ongoing development, in the meantime, is development of telecommunications by the wavelength multiplex transmission method for transmitting optical signals having different wavelengths from each other on one optical fiber. Use of an optical amplifier of the optical fiber amplifier type described above in an optical communication system of the wavelength multiplex transmission method (wavelength multiplex transmission system) is expected to further expand the channel capacity and realize long distance transmission.
A typical example of an optical amplifier of the optical fiber amplifier type described above is an EDFA (erbium-doped optical fiber amplifier). There are continuing endeavors to achieve wavelength multiplex transmission as above in which an EDFA is used and a transmission band is set in a wavelength range from 1525 nm to 1565 nm, for example, which is a gain band of an EDFA.
In order to use an EDFA for wavelength multiplex transmission, it is necessary that the dependency of the gain on the wavelength is small in a transmission band, i.e., a gain is uniform in the transmission band. However, as denoted at the characteristic curves a through c in FIG. 9, the gain of an EDFA is dependent on the wavelength in the transmission band. In FIG. 9, the characteristic curve a represents the dependency of the gain in an EDFA on the wavelength at 65xc2x0 C., the characteristic curve b represents the dependency of the gain in an EDFA on the wavelength at 0xc2x0 C., and the characteristic curve c represents the dependency of the gain in an EDFA on the wavelength at 25xc2x0 C., each in a wavelength range from 1530 nm to 1560 nm.
As described above, since an EDFA has a relatively large dependency of the gain on the wavelength, a sufficiently satisfactory result has not been obtained for high-quality wavelength multiplex transmission.
The present invention aims at providing an optical component which levels out the dependency of the gain on the wavelength of an EDFA in the wavelength range to be used. To this end, an optical component according to one aspect of the present invention has a structure as described below. That is, the optical component comprises:
a first long-period grating which is formed in an optical waveguide; and a second long-period grating which is formed in said optical waveguide, wherein said first and said second long-period gratings have different periods from each other, said first long-period grating has a peak wavelength whose amplitude waveform of optical transmission losses with respect to a wavelength is located on the shorter wavelength side than a transmission band, said amplitude waveform including said peak wavelength shifts depending on a temperature, said second long-period grating has a peak wavelength whose amplitude waveform of optical transmission losses with respect to a wavelength is located within said transmission band, said amplitude waveform including said peak wavelength shifts depending on the temperature, and due to temperature dependent shifts of said amplitude waveforms in said first and said second long-period gratings, a optical transmission loss value increases or decreases depending on the temperature, whereby the temperature dependent gain characteristic of an optical amplifier is compensated for in said transmission band.
Further, another aspect of the present invention aims at providing an optical component of a structure described below. That is, the optical component comprises first and second long-period gratings which are formed in an optical waveguide, wherein said first and said second long-period gratings respectively have unique optical transmission loss characteristics such that there are a plurality of optical transmission loss peak wavelengths of a first-order mode to an Nth-order mode which are apart from each other in terms of wavelength (where N is an integer equal to or larger than 2), the period of said first long-period grating is determined such that of the unique optical transmission loss peak wavelengths, a optical transmission loss peak wavelength of a preset-order mode is on the shorter wavelength side than a transmission band and that a optical transmission loss peak wavelength of a mode next to said preset-order mode is on the longer wavelength side than said transmission band, the period of said second long-period grating is determined such that of the unique optical transmission loss peak wavelengths, a optical transmission loss peak wavelength of a preset-order mode is on the longer wavelength side within said transmission band and that a optical transmission loss peak wavelength of a mode immediately precedent to said preset-order mode is on the shorter wavelength side than said transmission band, and amplitude waveforms, together with optical transmission loss peak wavelengths of said preset-order modes of said first and said second long-period gratings, shift toward the longer wavelength side or the shorter wavelength side depending on the temperature, and a optical transmission loss value increases or decreases depending on the temperature, whereby the temperature dependent gain characteristic of an optical amplifier is compensated for in said transmission band.